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Automotive Industry

The trends in CFD are continuous, dynamic, and real: a variety of new computational fluid dynamics software packages are just a mouse click away for part and product designers—with a lot more capability to boot!

Automotive Design & Production, Oct, 2004 by Lawrence S. Gould

For years, CFD vendors have taken the geometry from computer-aided design (CAD) to build the CFD model for analysis. But, says Thomas Marinaccio, director of CFD Consulting Services for software vendor CD adapco Group in Melville, NY, it's been a one-way transfer. "It's dead," he says, meaning the designer can't modify the geometry once it's inside CFD.

Funny, all the CFD vendors say their products are integrated to CAD. "That can mean several things," explains Judd Kaiser, technical solutions specialist for fluids and meshing at Ansys Canada Ltd (Waterloo, Ont., Canada). Does it provide good data transfer? Does it provide a clean translation of the CAD geometry to the CFD meshing environment? Does the parametric model automatically update when the CFD mesh updates? Does the integration truly provide two-way connectivity? That is, once an optimum solution is understood in CFD, can the designer push changes back into the CAD system?

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The key here, continues Kaiser, is that the shared geometry database can be used for finite element analysis (FEA; the structural side of analysis) and CFD (the fluid, thermal, acoustic, vibration, etc., side of analysis). "The key is connecting everything end-to-end and that it's all in the same environment. The minute you do a data transfer, you lose that parametric information. You lose the ability to drive optimization by connecting to those parameters from the analysis end," continues Kaiser.

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The latest version of CFX 5.7, Ansys' CFD system, has this capability in two ways. First, the company's Workbench is a user-friendly interface for not just FEA applications, but also for hosting meshing, a CAD interface, and CFD analysis. Of course, this integration is helped in that Ansys actually owns all of those software tools. Second, CFX 5.7 has a feature called "FSI" (fluid structure interaction). This is useful when the results of a fluids analysis changes the shape of a structure, and the structural analysis, in turn, affects the CFD calculation. Case in point: Fuel injectors and anti-lock braking systems, where fluid pressures are so high they actually deflect metal a little bit.

DELINKING CFD TO EXPENSIVE DESKTOPS

Earlier this year, CD adapco introduced a new CFD product: STAR-CCM+. "CCM" stands for "computational continuum mechanics"; it's sort of CD adapco's moniker for "multi-physics" analysis, and more. (Currently, the product includes analysis for a wide range of external and internal flows, including conjugate heat transfer and porous media modeling; a broad set of turbulence models; and a variety of boundary conditions.) The "and more" comes from a complete rewrite of the CFD package, which is now based on a client-server architecture, Java scripts, and C++.

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"With STAR-CCM+, it's like having [a big, expensive workstation] under my desk and I was doing the CFD analysis right here," explains Bill Clark, CD adapco's director of Engineering Software Business in Plymouth, MI. All the CFD can be launched, monitored, and displayed on a lightweight client machine, such as a wireless laptop. (Or a Palm Pilot or a Blackberry, posits Clark and Marinaccio.) This is possible because the client is similar to a web browser that has an operating system-independent, Java-based front-end. All the heavy CFD work, such as mesh generation, solving, and posting, is done on a big number-cruncher somewhere else (the server). The back-end software, the solver itself, is written in C++, an object-oriented programming language.

Moreover, adds Clark, the analysis is fully interactive. An analyst can start a CFD job at work, go home, log in from home, join the server, view how the simulation is going, make an assessment, and then, while the simulation is running, change parameters on-the-fly that might affect the job. Or, a team member can connect and modify the model--all without ever stopping the simulation, which would take the job out of queue and out of the number-crunching environment.

EASIER TO USE, AND MORE TO USE

Fluent Inc. (Ann Arbor, MI) recently debuted FloWizard, a complement to the company's flagship CFD product called "Fluent." "This is our first attempt at having a tool that's much easier to use," explains Stewart Featherstone, Fluent's Automotive Industry Team sales manager. "The idea here is to open CFD to more people and to compress the design cycle."

FloWizard is a flow simulation software package that prompts non-CFD experts through the process of taking a CAD model through CFD analysis--from CAD file import all the way to HTML output showing flow and heat transfer information, including full-color plots and animations of the flows. Users don't need extensive experience with complex 3D CAD models nor with CAE meshes. In fact, FloWizard alerts the user about suspicious inputs or questionable results. The analysis involves "some very complex physics," continues Featherstone, including 3D, incompressible, steady-state flows; laminar and turbulent flows; and convection and conduction heat transfer. It can handle pressures, velocities, mass flow rates, volumetric flow rates at inlets and outlets, and walls (with or without internal conduction) and moving belts.

Automotive Industry

The trends in CFD are continuous, dynamic, and real: a variety of new computational fluid dynamics software packages are just a mouse click away for part and product designers—with a lot more capability to boot!

Automotive Design & Production, Oct, 2004 by Lawrence S. Gould

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